Four-stroke internal combustion engine

ABSTRACT

A four-stroke internal combustion engine is provided that is capable of use in many power tools, including those power tools subjected to tippable applications. There is provided within an engine housing, an oil reservoir and a valve chamber which independently communicate with a crank chamber. A system of strategically placed dividers and passageways within the engine housing appropriately directs lubricant within the engine housing so that the internal cavity of the engine is lubricated during use in any operational attitude, and so that the lubricant flows to and is held in the proper chambers during storage. There is also provided a breather arrangement for an internal combustion engine which includes a camshaft having a hollow passageway in communication with a crank chamber.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application is a continuation of U.S. application Ser. No.09/600,096, filed Jun. 7, 2001, which is a §371 filing of InternationalApplication No. PCT/US00/00841, filed Jan. 13, 2000 and claimingpriority to U.S. Provisional Application No. 60/117,215, filed Jan. 25,1999. The entire contents of these prior applications are herebyincorporated by reference herein.

FIELD OF THE INVENTION

[0002] The present invention relates, generally, to four-stroke internalcombustion engines and, more particularly, to four-stroke internalcombustion engines used in trimmers, blowers, vacuums, chain saws, otherhand-held power tools, snowblowers, generators, vegetation cuttingdevices such as lawn mowers, or other outdoor power equipment.

BACKGROUND OF THE INVENTION

[0003] Many hand-held power tools or other outdoor power equipment arepowered by electric motors or two-stroke internal combustion engines.Electric motors are limited to certain applications due to the availablepower for products utilizing a cord, and battery longevity for cordlessproducts. Conventional two-stroke engines include a lubricating means inwhich the lubricant is mixed with fuel which allows the engines tooperate in any given position such as upright, inclined, sideways orupside down. For example, when using a chain saw, the chain saw istypically capable of use in either an upright, sideways or upside downcondition. Over the past few years, there has been a requirement byvarious governing bodies to reduce the emissions associated with allsmall gas engines, particularly, conventional two-stroke engines. Thus,because four-stroke engines do not require the mixing of lubricant andfuel, it is desirable to use four-stroke engines in place ofconventional two-stroke engines, since four-stroke engines normallyrelease fewer undesirable emissions as compared to the amount ofundesirable emissions released by conventional two-stroke engines.

[0004] However, previously, it was widely viewed that four-strokeinternal combustion engines could only be used for limited applications,such as lawn mowers, snowblowers, generators, or other portable productshaving wheels. It was thought that these prior four-stroke engines weretoo heavy and cumbersome to be used in operator-carried power tools.Moreover, since it is generally necessary to store oil separate from thegas so that the oil can be used for lubrication, traditional low-costfour-stroke engines were not designed to operate in any position otherthan a substantially upright position because if the engine wassignificantly tipped or tilted, the lubricant would foul the engine.Only very recently has it been contemplated that a four-stroke enginemay be used in a hand-held power tool or in other applications where theengine may operate in a tipped or tilted condition.

SUMMARY OF THE INVENTION

[0005] Accordingly, there is a need for a four-stroke internalcombustion engine that is capable of use in various power tools, and yetis also capable of having low emissions and being sufficiently light tobe carried by an operator when desired. What is also needed is afour-stroke internal combustion engine that is capable of operating inmany different attitudes of the engine. What is also needed is afour-stroke engine that eliminates the need for an elaborate lubricationsystem. What is needed is a four-stroke internal combustion engine whichaccomplishes these features and other features and which is alsoeconomical to manufacture.

[0006] In one embodiment of the present invention, there is provided afour-stroke internal combustion engine, preferably a side valve or “L”head engine, having an engine housing which includes a crankcase and acylinder. A cylinder head which at least partially defines a combustionchamber is positioned adjacent to the cylinder. An intake valve and anexhaust valve are disposed within the engine housing. A crank chamberand an oil reservoir are disposed within the crankcase in such a waythat the oil reservoir is in fluid flow communication with the crankchamber. A strategically placed agitator, located at least partiallywithin the crank chamber, moves lubricant within the engine housingduring operation of the engine to lubricate the necessary components ofthe engine.

[0007] A divider is disposed within the crankcase to at least partiallydivide the crank chamber and the oil reservoir. The divider assists indirecting the lubricant during operation and storage of the engine inorder to prevent a substantial amount of lubricant from undesirablymigrating into the combustion chamber when the engine is operated orstored in an upright or tilted position. In one aspect of the presentinvention, the divider defines a path which extends about the divider.The path allows lubricant in the oil reservoir to flow around asubstantial portion of the divider to further enhance the lubricatingand storage features of the engine according to the principles of thepresent invention.

[0008] The engine is constructed of light weight material andappropriately sized so that the engine is sufficiently light enough tobe usable in hand-held power tools. Thus, the four-stroke internalcombustion engine according to the present invention may be utilized inthose applications which are traditionally limited to the use oftwo-stroke internal combustion engines.

[0009] In one aspect of the present invention, the divider includes atleast one opening such that the crank chamber and the oil reservoir arein fluid flow communication through the opening. The opening helpsensure that the crank chamber is substantially continuously lubricatedduring operation of the engine, even if the engine is operated under atilted condition. The opening in the divider is positioned such that atleast some of the lubricant found in the crank chamber after operationof the engine may flow back into the oil reservoir even if the engine isstored in a tilted state. Preferably, the divider includes a pluralityof openings.

[0010] In another aspect of the present invention, the engine housingfurther includes a cylinder side wall which at least partially extendsinto the crank chamber to define a lubricant receiving space between thedivider and the cylinder side wall. Preferably, the cylinder side wallat least partially defines a piston bore. During operation, as theagitator mixes and slings lubricant around the inside cavity of theengine as a result of the rotating action of the agitator, the lubricantis more likely to be slung into the open area between the divider andthe cylinder side wall rather than into the piston bore. Moreover,during storage, the open area or lubricant receiving space providesadditional space for the lubricant to be held if the engine is stored ina sideways or upside down position to also prevent a substantial amountof the lubricant from flowing into the piston bore. As previously noted,migration of the lubricant into the combustion chamber leads to anunwanted condition. A function of the lubricant receiving space is toinhibit lubricant from reaching the piston bore, thereby preventing asubstantial amount of lubricant from reaching the combustion chamber.

[0011] In another aspect of the present invention, the engine housingfurther includes a valve chamber. The intake valve and exhaust valve aredisposed within the valve chamber and the valve chamber is in fluid flowcommunication with the crank chamber. The operation of the agitator, thepressure pulses created within the engine during operation of theengine, the communication of the oil reservoir with the crank chamber,and the communication of the crank chamber with the valve chambertogether allow the working components found within the valve chamber tobe lubricated, even if the engine is operated in a tilted manner.Preferably, the valve chamber is also in fluid flow communication withthe cylinder side wall to further enhance the lubrication of the workingcomponents located within the valve chamber. The strategic positioningof the fluid flow openings into the valve chamber will prevent the valvechamber from receiving too large of a quantity of lubricant when theengine is being operated or being stored.

[0012] In another embodiment of the present invention, the engineincludes a cantilevered crankshaft which has opposite ends and which issubstantially located within the crank chamber. The agitator includes acounterweight which is interconnected to the cantilevered end of thecrankshaft. The counterweight is adapted to reduce windage resistance onthe crankshaft and to sling lubricant about the crank chamber as thecrankshaft rotates during operation of the engine. Further, thecounterweight throws the lubricant away from the main bearings of thecrankshaft, thereby substantially preventing the main bearings frombeing flooded by the lubricant during operation of the engine. Thedivider may be provided with a scraper which is used to limit the amountof lubricant which comes into contact with the agitator or thecounterweight. The scraper preferably at least partially extends intothe crank chamber, so that as the agitator rotates past the scraperduring operation of the engine, the scraper meters the amount oflubricant which comes into contact with the agitator.

[0013] In another aspect of the present invention, a cam shaft disposedsubstantially normal to the crankshaft is rotatably driven by thecrankshaft. The substantially normal arrangement of the cam shaft andcrankshaft enables the engine to be longer in a direction parallel to apower take off, as compared to a conventional engine in which the camshaft is parallel with the crankshaft. Such an engine is desirable incertain hand-held power tool applications, such as power trimmers, inorder to provide an overall better balance of the power tool for theconvenience of the user. The substantially normal arrangement of theshafts also allows for an intake port and an exhaust port disposed inthe cylinder to be significantly spaced apart. Segregating the portswill reduce heat migration from the exhaust port to the intake portwhich could result in hot restart (e.g., vapor lock) problems.

[0014] Preferably, the intake and exhaust ports are elliptical in shape.The elliptical configuration of the ports enables the overall profile orheight of the engine housing to be reduced, thereby reducing the amountof material needed for the overall engine housing. This helps reduce theoverall weight of the engine housing. The port walls are provided withsufficient surface area and strength to support the portion of theengine housing and cylinder head disposed above the ports. Thesubstantially normal relationship between the crankshaft and the camshaft also allows the valves to be disposed substantially normal to thecrankshaft. A first valve tappet associated with the intake valve and asecond valve tappet associated with the exhaust valve operatively engagethe cam shaft to provide for the proper operation of the valves withrespect to a four-stroke internal combustion engine. Such a compactarrangement further limits the overall weight of the engine.

[0015] In another embodiment of the present invention, a breatherarrangement for the four-stroke internal combustion engine is provided.The cam shaft is provided with an axial passageway and several radialapertures. The radial apertures communicate with the crank chamber andthe passageway. A breather tube communicates with the passageway and anair intake system of the engine. A check-valve is positioned between theend of the cam shaft and the air intake system to maintain the negativepressure created within the engine. Blow-by gas inside the engine isadmitted into the radial aperture of the cam shaft and is sent throughthe axial passageway of the cam shaft and into the breather tube, sothat the blow-by gas is recirculated within the engine. The pressurepulses created within the engine cause the blow-by gas to enter the camshaft and be recirculated as described. However, the centrifugal actionof the cam shaft counters the action created by the pressure pulses,thereby substantially preventing the heavier lubricant, as compared tothe blow-by gas, from entering the radial apertures in the cam shaft. Asa result, the lubricant will substantially remain within the cavity ofthe engine and will not travel through the breather tube to the airintake system of the engine.

[0016] In another aspect of the present invention, the engine housing isdesigned to cooperate with a piston found within the piston bore suchthat a connecting rod can be conveniently attached to the piston and thecrankshaft. The crankcase and the piston each include an access hole. Aconnecting rod is operatively attached to the crankshaft and the pistonin the following manner. The access hole in the crankcase and the accesshole or aperture in the piston are aligned during installation of awrist pin. The wrist pin is inserted into the piston aperture andthrough an end of the connecting rod to connect the connecting rod tothe piston. A star washer is used to hold the wrist pin in place afterinstallation.

[0017] The compact size of the engine according to the present inventionand the cantilevered crankshaft make it difficult to assemble theinternal components of the engine, such as the piston-connectingrod-crankshaft assembly. The cooperation of the access holes in thecrankcase and the piston allow for easy assembly of thepiston-connecting rod-crankshaft assembly. Preferably, it is desirableto use the same engine housing casting for engines having differenthorsepower ratings, simply by changing the connecting rod and thus, thelength of the piston throw. To facilitate assembly and to permit thesame engine housing casting to be used for different sized engines, anelliptical, or the like, wrist pin boss is formed in the crankcase ofthe engine housing. The wrist pin boss can be machined at its upper endto provide an access hole in the crankcase for a first horsepower ratingor piston throw, and the wrist pin boss can be machined at its lower endto provide an access hole in the crankcase for a second horsepowerrating or piston throw. After the wrist pin boss is properly machined,the wrist pin-which connects the piston to the connecting rod-isinserted through the crankcase aperture and into the piston aperture aspreviously explained. In this way, the same engine housing casting canbe used for different sized engines.

[0018] In another aspect of the present invention, the crank chamberincludes at least two bearing pockets. One of the pockets has a largerdiameter than the other. Both of the bearing pockets are disposed on thesame side of the internal cylinder side wall. The cantileveredcrankshaft is supported by two main bearings located in the respectivebearing pockets. The bearing pocket nearest the cantilevered (input) endof the crankshaft is the larger diameter bearing pocket so that thebearing pockets can be machined in the crank chamber from the same sidewith a single tool thereby eliminating unnecessary tooling requirements.This provides a significant savings in capital costs and manufacturingexpenses. Preferably, before assembling the crankshaft in the crankchamber, the outer bearing and then the agitator or counterweight areproperly positioned around the cantilevered end of the crankshaft. Thecounterweight is provided with an access aperture in order to allow atool to appropriately contact the adjacent bearing and the crankshaft.In this way, as the crankshaft is placed into the crank chamber, thebearing is not damaged and the crankshaft is properly positioned.

[0019] In another aspect of the present invention, the combustionchamber is adapted to enhance swirl of the air/fuel mixture to increaseefficiency of the engine. Preferably, a spark plug is positioned closerto the exhaust valve than the intake valve to also improve engineefficiency, and reduce the likelihood of self-ignition within theengine.

[0020] In another aspect of the present invention, the engine housing isdesigned in such a way so as to permit two engine housings to beproduced using only one die tool and one die casting machine. This alsoreduces capital costs and manufacturing expenses.

[0021] In another aspect of the present invention, a starter assembly isattached to the rear of the engine and is designed to utilize acrankshaft pin which is integral with the crankshaft. The crankshaft pinis the contact point for the internal rotation of the crankshaft inorder to start the engine.

[0022] In another aspect of the present invention, the blower housinghas an inwardly extending hub. The hub fits over the crankshaft. Thestarter assembly slides onto the hub. A star washer or the like isplaced over the hub so as to prevent the axial movement of the starterassembly, particularly the pulley. This arrangement eliminates the needfor separate mounting bosses and fasteners which are normally needed toattach the starter assembly to the blower housing and which typicallyblock the cooling air flow by the fan.

[0023] In another aspect of the present invention, a shroud is providedto at least partially surround the engine housing. The shroud isprovided with a pair of opposed channels. A fuel tank having opposed,outwardly extending shoulders is held by the shroud as the shoulders arereceived by the respective channels. Preferably, a filler material ispositioned between each of the channels and respective shoulders so asto provide a more snug fit between the shroud and the fuel tank.

[0024] In a preferred embodiment, a fuel line includes a fuel filterattached to the end of the fuel line disposed within the fuel tank. Thefuel filter acts as a weight. During operation of the engine, as theengine is tipped in different orientations, the weighted fuel lineswings to the bottom of the fuel tank so that fuel is always picked upby the fuel line regardless of the orientation of the engine.

[0025] In one aspect of the present invention, the shroud includes anopening around the intake port. An intake isolator is provided having anair/fuel passageway extending therethrough. The intake isolator ismounted to the engine housing so that the air/fuel passageway of theintake isolator is aligned with the intake port. Further, the intakeisolator is positioned within the opening of the shroud to substantiallyensure that cooling air passing between the engine housing and theshroud cannot escape through the opening in the shroud. The intakeisolator is also used to insulate the intake air/fuel mixture from thesurrounding environment to the extent feasible to ensure that theair/fuel ratio remains substantially correctly calibrated. In oneembodiment of the present invention, a carburetor is interconnected withthe intake isolator.

[0026] In one aspect of the present invention, the shroud includes aplurality of raised portions on one side thereof. If desired, the enginecan be placed on the ground to rest on the raised portions. This couldbe useful, for example, on a trimmer when the user desires to change thecutting line located on the end of the shaft which is spaced asignificant distance from the engine.

[0027] In another aspect of the present invention, the engine housingincludes a back plate which is adjacent to a flywheel. Preferably, thecrankcase, the cylinder and the back plate are cast as a singlecomponent, thereby reducing manufacturing and assembly costs, andthereby limiting the overall size of the engine housing. In a preferredembodiment, the engine housing further includes at least one finintegrally formed thereto. The fin extends from the back plate andbeneath the crankcase to increase the stability between the back plateand the crankcase. The fin also is adapted to help cool the enginehousing, particularly, the crankcase.

[0028] In another aspect of the present invention, a muffler isconnected to the engine housing. The muffler includes a boss whichextends into the exhaust port. In one embodiment, the engine housingincludes an angled, stepped sealing surface located in the exhaust port.The end of the muffler boss mates against the exhaust port sealingsurface to substantially prevent the exhaust from undesirably escapinginto the surrounding atmosphere. Preferably, a sealing gasket ispositioned between the end of the boss and the exhaust port sealingsurface to even better prevent the exhaust from undesirably escapinginto the atmosphere. In another embodiment, the muffler boss issurrounded by a portion of the exhaust port to define a clearancebetween the outside liner of the boss and the adjacent surface of theexhaust port. A gasket is positioned between the muffler and the enginehousing to seal the clearance space between the muffler and the enginehousing so as to prevent exhaust from undesirably escaping into theatmosphere. In a preferred embodiment, the gasket is an enlarged gasketwhich also serves as a heat shield between the engine housing and theuser.

[0029] In one aspect of the present invention, the muffler includes apair of outer shells having a pair of mounting bolt holes extendingtherethrough for receiving a pair of mounting bolts. A pair of boltreceiving bores are located on opposite sides of the exhaust port in theengine housing. This arrangement ensures that the muffler will besecurely attached to the engine housing in a stable manner. In apreferred embodiment, the muffler includes an inner shell sandwichedbetween the outer shells. The inner shell is a baffle plate adapted toreduce the amount of exhaust admitted into the atmosphere. The innershell also includes a pair of mounting bolt holes to receive themounting bolts. In yet another preferred embodiment, one of the outershells includes a shoulder extending around an edge of the outer shell.The other outer shell includes a hook-shaped flange extending around anedge of the outer shell. The hook-shaped flange of the one outer shellreceives the shoulder of the other outer shell upon assembly of themuffler. The assembly is such that if exhaust leaks out of the muffler,the exhaust will leak away from the engine housing so as not tosubstantially heat the engine housing.

[0030] In one aspect of the present invention, the four-stroke internalcombustion engine includes an engine housing having an integrally formedcrankcase, cylinder and flywheel back plate. The flywheel back plateincludes at least one mounting boss on one side and at least one othermounting boss on an opposite side. An assembly fixture is utilized tohold the engine housing during assembly of the engine. Each mountingboss on the flywheel back plate receives a separate pin of the assemblyfixture to secure the engine housing to the assembly fixture. A shroudis provided to at least partially surround the engine housing. Theshroud includes at least two slots such that the slots surround the pinsof the assembly fixture when the shroud is positioned around the engine.The shroud can then be firmly attached to the engine. After the shroudis attached to the engine, the pins can be removed from the mountingbosses. In this manner, the engine can be substantially completelyassembled while the engine is mounted to the assembly fixture.

[0031] Accordingly, it is a principal feature of the present inventionto provide a four-stroke internal combustion engine which includes asimple and inexpensive lubricating system which enables the engine to befunctional in various operational attitudes.

[0032] It is a feature of the present invention to provide a four-strokeengine incorporating the foregoing features and yet also simple and easyto manufacture and assemble.

[0033] Other features and advantages of the invention will becomeapparent to those skilled in the art upon review of the followingdetailed description, claims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is an exploded perspective view of a four-stroke internalcombustion engine according to the present invention.

[0035]FIG. 1A is a perspective view of the four-stroke engine of FIG. 1illustrating the engine as assembled for use with, e.g., a powertrimmer.

[0036]FIG. 2 is a cross-sectional end view and a partial schematic viewof the engine of FIG. 1 taken along line 2-2 of FIG. 3.

[0037]FIG. 3 is a cross-sectional side view of the assembled engine ofFIG. 1.

[0038]FIG. 4 is an enlarged view of a portion of the engine shown inFIG. 3 illustrating the rotational relationship between a cam gear and acrank gear, a portion of a lubricant flow path, and a portion of abreather system for the engine shown in FIG. 1.

[0039]FIG. 5 is an enlarged view of a portion of the engine shown inFIG. 3 illustrating a piston in its bottom dead center position.

[0040]FIG. 6 is a schematic representation illustrating another aspectof the present invention which concerns the attachment of a connectingrod to a piston and a crankshaft.

[0041]FIG. 7 is a perspective front view taken along line 7-7 of FIG. 9illustrating a counterweight positioned adjacent to a main bearing ofthe crankshaft.

[0042]FIG. 7A is a side view of the counterweight of FIG. 7.

[0043]FIG. 7B is another perspective view of the counterweight of FIG.7.

[0044]FIG. 8 is a perspective view illustrating an agitator cooperatingwith a scraper found on a wall within the engine cavity in order toregulate the amount of lubricant which comes into contact with theagitator.

[0045]FIG. 8A shows the rotational movement of the agitator of FIG. 8and how the scraper controls the lubricant which comes into contact withthe agitator.

[0046]FIG. 9 is a schematic representation of another aspect of thepresent invention illustrating the positioning of a crankshaft within acrank chamber disposed in an engine housing.

[0047]FIG. 10 is a partial schematic view of a top portion of the enginehousing taken along line 10-10 of FIG. 3 illustrating the spatialrelationship between a combustion chamber, a piston bore, an intakevalve and an exhaust valve.

[0048]FIG. 11 is a partial schematic view of a cylinder head taken alongline 11-11 of FIG. 3 illustrating the spatial relationship between thecombustion chamber, the piston bore, the intake valve, the exhaust valveand portions of a spark plug.

[0049]FIG. 12 is a schematic view illustrating the path of an air/fuelmixture through an intake system to the combustion chamber and the pathof the exhaust out of the combustion chamber through an exhaust systemin an engine according to the present invention.

[0050]FIG. 13 is a cross-sectional partial schematic view of an engineaccording to the present invention showing the state of the lubricant inthe crank chamber and an oil reservoir when the engine is in an upsidedown state.

[0051]FIG. 14 is a cross-sectional view of another embodiment of thepresent invention showing a starter assembly attached to the rear of afour-stroke internal combustion engine.

[0052]FIGS. 15-18 are schematic representations of two engine housingswhich are capable of being produced using one die tool and one diecasting machine.

[0053]FIG. 19 is a schematic view of a power trimmer in which anotherfour-stroke internal combustion engine according to the presentinvention is employed.

[0054]FIG. 20 is a perspective view of a shroud which at least partiallysurrounds an engine, wherein the shroud is adapted to enhance overallassembly operations of the engine.

[0055]FIG. 21 is an exploded partial perspective view of the four-strokeengine of FIG. 19.

[0056]FIG. 22 is another exploded partial perspective view of thefour-stroke engine of FIG. 19.

[0057]FIG. 23 is a perspective view of an engine housing with a mufflerattached thereto.

[0058]FIG. 24 is an exploded perspective view of FIG. 23.

[0059]FIG. 25 is a perspective view illustrating the flywheel end of theengine housing of FIG. 23.

[0060]FIG. 26 is an enlarged partial cross-sectional view taken alongline 26-26 of FIG. 23 illustrating a connection between the enginehousing and muffler of FIG. 23.

[0061]FIG. 27 is an alternative connection between the engine housingand muffler of FIG. 26.

[0062]FIG. 28 is a perspective view of the engine housing of FIG. 23without the muffler.

[0063]FIG. 29 is a front view of an intake isolator as shown in FIG. 22and FIG. 20.

[0064]FIG. 30 is a cross-sectional view of the intake isolator of FIG.29.

[0065]FIG. 31 is a partial cross-sectional side view of the assembledengine of FIGS. 21 and 22.

[0066]FIG. 32 is an enlarged view of a portion of the engine shown inFIG. 31 illustrating a piston in its bottom dead center position.

[0067]FIG. 33 is an enlarged view of the relationship between the shroudand starter assembly in terms of retaining the starter assembly on theshroud.

[0068]FIGS. 34-38 illustrate various views of the starter pulley shownin FIG. 33.

[0069]FIGS. 39-40 are schematic representations of two engine housingswhich are capable of being produced using one die tool and one diecasting machine.

[0070] Before the embodiments of the invention are explained in detail,it is to be understood that the invention is not limited in itsapplication to the details of construction and the arrangements ofcomponents set forth in the following description or illustrated in thedrawings. The invention is capable of other embodiments and of beingpracticed or of being carried out in various ways. Also, it is to beunderstood that the phraseology and terminology used herein is for thepurpose of description and should not be regarded as limiting.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0071] Illustrated in FIG. 1A of the drawings is a four-stroke internalcombustion engine 20 according to the present invention. The engine 20drives a conventional shaft typically housed in a shaft tube 22 which inturn drives an implement having a rotary head, cutting filament orblade, rotary impeller, or the like, depending on the type of power toolin use (see, e.g., FIG. 19). The shaft arrangement shown in FIG. 1A (andFIG. 19), typically used in conjunction with a hand-held power trimmer,is used for illustrative purposes only and it should be understood thatother power tools such as those mentioned previously herein are capableof utilizing the four-stroke engine of the present invention. In otherwords, generally, the engine according to the present invention ispreferably used in an orientation where the implement or working toolhas an axis which is substantially parallel with a crankshaft axis. Theengine according to the present invention may also be orientated withthe crankshaft being horizontal or vertical. The engine according to thepresent invention is particularly well suited for those applications inwhich high RPMs, e.g., 3,000 RPMs up to 7,000-8,000 RPMs or more, may berequired and in which an output of less than 1 to over 6 horsepower maybe supplied. Importantly, whichever type of power tool is used incombination with the four-stroke engine according to the presentinvention, the engine is capable of working, at least temporarily, insubstantially any operational position of the power tool.

[0072] Illustrated in FIG. 1 of the drawings is an exploded perspectiveview showing various components of the four-stroke internal combustionengine 20 according to the present invention. Shown in FIG. 1 is a sidevalve or “L” head engine in which the various features of the presentinvention are employed. Side valve engines are sometimes referred to as“L” head engines because of the positional relationship of an intakevalve and an exhaust valve with respect to a combustion chamber. As willbe apparent below, the “L” is in reference to the path taken by anair/fuel mixture and the exhaust through respective valves and portsfound in the engine body. Also, importantly, in an “L” head engine, theintake valve port and the exhaust valve port are located in the enginehousing, not in the cylinder head which is generally common to overheadvalve or overhead cam engines.

[0073] Before describing in detail the various features of the presentinvention, the components shown in FIG. 1 are identified for the sake ofclarity. Shown are an ignition coil screw 24 used to attach an ignitioncoil (not shown) to the engine 20; shroud screws 27 attach shroud 26 toan engine housing 28; cover screws 30 attach sump cover 32 and sumpcover gasket 34 to the engine housing 28 in order to seal one end of theengine housing 28; cylinder head screws 36 attach cylinder head 38 andcylinder head gasket 40 to the engine housing 28 thereby at leastpartially defining a combustion chamber 39 (FIG. 2); carburetor 42 andmuffler 44 are appropriately connected to the engine 20; carburetor 42cooperates with intake port 41 and air cleaner or filter 43 (FIG. 2);muffler 44 cooperates with exhaust port 45; flywheel 46 which includesan integral fan (not shown) is positioned between the shroud 26 andengine housing 28 with the help of a flywheel key (not shown) in orderto cool the engine 20 during operation; piston 48 is received by pistonbore 50 within engine housing 28; intake valve 52 and exhaust valve 54are positioned adjacent piston bore 50 within engine housing 28; intakevalve seat 56 and exhaust valve seat 58 are placed within engine housing28 to cooperate with the respective heads of valves 52 and 54; valvesprings 60 are placed in a valve spring chamber and held within thevalve spring chamber by valve spring keepers 62; the valve springchamber is sealed by valve cover 64 and valve cover gasket 66;crankshaft bearing 68, crankshaft bearing 70, worm-helical or spiralgear 74, counterweight 76, crank pin 78 and crankshaft 80 are part ofcrankshaft assembly 82; counterweight 76 includes an aperture 77;connecting rod 84 includes connecting rod bearings 86 and 88; one end ofconnecting rod 84 fits over crank pin 78 and a wrist pin 90 connects theother end of connecting rod 84 to piston 48 by sliding in aperture 92 ofpiston 48; wrist pin 90 cooperates with access hole 93 of engine housing28 when attaching the connecting rod 84 to the piston 48; cam shaftbushing 94, cam shaft bushing 96, cam shaft 98, cam lobes 100 and 102(FIG. 2), and worm-helical or spiral gear 104 are part of cam shaftassembly 106; cam cap 108 and cam cap gasket 110 are attached to enginehousing 28 by cam cap screws 111 in order to seal cam shaft assembly106; tappets 112 are properly positioned within the engine 20 tocooperate with valves 52 and 54; spark plug 114 is positioned in a sparkplug hole within cylinder head 38; divider 116 having slots 118, 120 and122 is disposed within engine housing 28 and at least partially definesa crank chamber 124 and a lubricant or oil reservoir 126; and the pistonbore 50 includes an extension 128 which at least partially extends intocrank chamber 124.

[0074] Other components and features not clearly shown in FIG. 1 will bedescribed below according to the features of the present invention.

[0075]FIG. 1 shows the carburetor 42 and the exhaust muffler 44 mountedon opposite sides of the engine housing 28. The carburetor 42 may be ofany type of carburetor that is tippable such as a standard variableventuri diaphragm carburetor found in small gas engines, but a rotaryvalve carburetor available from, e.g., Walbro, is particularly wellsuited for use in an engine according to the present invention. The aircleaner or filter 43 (schematically shown in FIG. 2) is mounted in ornear an inlet of an intake passage in the carburetor 42. A fuel tank(not shown in FIG. 1) is mounted typically to a lower surface of theengine housing 28 and cooperates with the carburetor 42 so that fuel andair can be supplied to the intake port 41 (FIG. 2) in the enginehousing.

[0076] The engine housing 28 is typically made of a lightweight aluminumalloy casting having a cylindrical bore or piston bore 50 formedtherein. As noted, the piston bore 50 is configured to partially extendinto the crank chamber 124 disposed within the engine housing 28. Thearea or space 136 (FIG. 13) between the extended piston bore 50 anddivider 116 accepts volumes of the lubricant or oil during operation andstorage to prevent too much lubricant or oil from entering the pistonbore 50 or valve chamber 156 (FIG. 2). The piston 48 is preferablycoated, such as with an iron coating, or chrome plated so as toeliminate the need for a sleeve such as an iron sleeve within the pistonbore 50. Alternatively, piston bore 50 may include an iron cylindersleeve.

[0077] The divider preferably includes bottom slot 118 which is locateddirectly below the piston bore 50. Optional side slots 120 and 122 ofthe divider 116 may be located substantially directly across from oneanother at a predetermined distance from the bottom of the piston bore50. The slots 118, 120 and 122 may be replaced with one or more holes orother apertures. As noted, the present invention is, of course, notlimited to a particularly sized engine, but may be used with anyinternal combustion engine. The design considerations to determine thesize and location of the slots or holes will be apparent below. Theslots or holes should be configured for different sized engines takinginto consideration the various features of the present invention.

[0078]FIGS. 8 and 8A show another aspect of the divider 116. Inoperation, as shown, the counterweight 76 is caused to rotate in onedirection, usually, a clockwise direction. The bottom slot 118 includesopposing sides 130 and 132. The second side 132, with respect to thedirection of travel of the counterweight 76, has a scraper 134 adjacentthereto. Preferably, the scraper 134 is positioned within 0.020 to 0.060inches of the counterweight 76 when the counterweight 76 is locatedclosest to the scraper 134. The scraper 134 limits or meters the amountof lubricant or oil (shown in broken dotted lines) which comes intodirect contact with the counterweight 76. The scraper 134 helps to limitthe amount of lubricant or oil which may be slung into the piston bore50 during operation and reduces the wind resistance caused by excessivelubricant on counterweight 76. It should be noted that the scraper 134could be configured in other ways. For example, bottom slot 118 in thedivider 116 could be a diagonal slot such that the second side of thediagonal slot acts as the scraper 134 but the scraper is not a raisedscraper as shown in FIGS. 8 and 8A. Alternatively, the bottom slot 118in the divider 116 could be a straight slot without the use of ascraper.

[0079] As noted, FIG. 1 shows the oil reservoir 126 disposed within theengine housing 28 defined by the divider 116 and the engine housing 28.The oil reservoir 126 is in fluid flow communication with the crankchamber 124, preferably through slots 118, 120 and 122. As shown, theoil reservoir 126 and the divider 116 are substantially curved orU-shaped. The divider 116 is preferably curved to direct lubricant awayfrom the piston bore 50 when the engine is tipped or inverted. Thecommunication between the two chambers 124 and 126 allows for the crankchamber 124 to be properly lubricated during use as the lubricant isallowed to flow between the two chambers 124 and 126 during use, and forthe lubricant to flow back into the oil reservoir 126 during storage sothat an excessive amount of lubricant does not adversely flow into thepiston bore 50.

[0080] Referring to FIGS. 1 and 3, crankshaft 80 is mounted within thecrank chamber 124. The crankshaft worm-helical or spiral gear 74 drivesthe cam shaft assembly 106. Worm-helical or spiral gears are commonlyknown in the art and readily available from any number of gearmanufacturers and suppliers. The crankshaft 80 and gear 74 may bemanufactured in any number of known ways. However, injection molding thegear around a trim metal piece representing the crankshaft would workwell according to the principles of the subject invention. The injectionmold material may be a thermoplastic material or nylon material known tothose skilled in the art. Another alternative is to provide a metalcrankshaft with an enlarged cylindrical piece of metal on the crankwhere a worm-helical or spiral gear is intended to be located. Thecrankshaft then is subjected to a hobbing procedure in which the gear ismachined on the crankshaft.

[0081] Still referring to FIGS. 1 and 3, bearings 68 and 70 arepositioned around the crankshaft 80 in order to support the cantileveredcrankshaft 80 when it is placed within the crank chamber 124. Thebearings 68 and 70 are placed on opposite sides of the worm-helical orspiral gear 74 and on the same side of the piston bore 50. The innerbearing 68 is smaller in diameter than the outer bearing 70. Thebearings 68 and 70 are dimensioned in this manner such that the bearingpockets found in the crank chamber 124 are machined from one side of theengine housing 28 using only one tool. As can be appreciated by thoseskilled in the art, machining bearing pockets from one direction reducesequipment, time and expense usually associated with having to machinebearing pockets from different directions.

[0082] As shown in FIG. 1, counterweight 76 is mounted on one end of thecrankshaft 80. FIGS. 7, 7A and 7B show in greater detail the shape andcontours of the counterweight 76. As generally understood, the forcesresulting from the operation of the piston 48, the connecting rod 84 andthe associated components, are balanced by the counterweight 76.Depending on the size of the engine, more than one counterweight may benecessary. The counterweight 76 includes wing-tipped aerodynamic sides138 and 140. Each wing-tipped side includes a back 142 that ispositioned adjacent the main bearing 70 and a front 144 opposite theback 142. The wing-tipped sides 138 and 140 have contoured surfaces thatextend from the back 140 to the front 142 of the counterweight 76. Inthis way, as will be more evident below, the aerodynamic shape of thecounterweight 76 assists in reducing air resistance on the counterweight76, generating the proper turbulence of air and lubricant within theinternal cavity of the engine 20 and directing the lubricant within theinternal cavity of the engine 20.

[0083] The tool access hole or aperture 77 of counterweight 76 (FIG. 7)is used for positioning the crankshaft 80 within the crank chamber 124.FIGS. 7 and 9 schematically show a tool 146 which is used to positionthe outer bearing 70, counterweight 76 and the crankshaft 80 within thecrank chamber 124. Bearing 68 is press fitted into the crank chamber 124and is adapted to receive one end of the crankshaft 80. Once thecrankshaft 80 has been manufactured, the bearing 70 is press fitted ontothe crankshaft 80. The counterweight 76 is then fixed to the crankshaft80. FIG. 7A illustrates a step 141 which provides a clearance ofapproximately 0.050 of an inch between the counterweight 76 and bearing70. As shown in FIG. 7, only portions 69 of the outside race of the mainbearing 70 are exposed after the counterweight 76 is placed on thecrankshaft 80. The access aperture 77 allows the tool 146 (FIG. 9) tocontact the outside race of the main bearing 70 in three spots whenassembling the crankshaft 80 and associated components of the crankshaftassembly 82 into the crank chamber 124. A fourth leg of the tool (FIG.9) contacts the cantilevered end of the crankshaft 80. This assemblyhelps ensure that the main bearing 70 will not be damaged upon assemblyand the crankshaft 80 will be properly seated when inserted into thecrank chamber 124.

[0084]FIG. 6 schematically illustrates how the connecting rod 84 isattached to the crankshaft 80 and piston 48. A custom shoulder bolt (notshown) may be utilized to affix the connecting rod 84 to the crank pin78. The entire crankshaft assembly 82 (FIG. 1) is mounted within thecrank chamber 124 (FIG. 3). The piston 48 is slid into the piston bore50 from the top of the engine housing 28. The aperture 92 in the piston48 is lined up with the access aperture 93 in the engine housing 28. Theconnecting rod 84 is attached to the crankshaft assembly 82 by virtue ofcrank pin 78 and positioned within a cut out portion 148 of the piston48. The wrist pin 90 is inserted through the access hole 93 of theengine housing 28 into the access hole 92 of the piston 48 and throughthe bearing 86 of the connecting rod 84. Since the aperture 92 of thepiston 48 is not drilled all the way through the piston 48, one end ofthe wrist pin 90 abuts an inner portion 150 of the piston 48. The wristpin 90 can be held in place within the piston 48 by a star washer 151inserted in the open end of the aperture 92 (see also FIG. 5).Preferably, the wrist pin 90 and the crank pin 78 are hollow so as toreduce the overall weight of the reciprocating mass which in turn meansa smaller counterweight with less weight is needed to balance the forcesgenerated by the reciprocating mass. Reducing the overall weight of thereciprocating components improves vibration and makes the engine lighterfor ease of operation.

[0085] The cam shaft 98, the eccentric style cam lobes 100 and 102 andthe cam gear 104 are shown as separate parts in FIG. 2. It should benoted that these parts can be injected molded as a single componentusing, for example, a thermoplastic or nylon material. Alternatively,certain components may be injected molded around a piece of trim metalto create the final assembly in similar manner to that contemplated forthe crankshaft 80 and worm-helical or spiral gear 74.

[0086]FIG. 2 illustrates that the cam shaft 98 includes a passageway152. FIGS. 2, 3 and 4 show that a portion of the cam shaft assembly 106(FIG. 1) adjacent the worm-helical or spiral gear 104 includes at leastone radial aperture 154 exposed to the passageway 152 and crank chamber124. The passageway 152 and aperture 154 may be drilled into the properportions of the cam shaft assembly 106 or molded therein. Essentially,the passageway 152 and the aperture 154 and cam shaft assembly 106cooperate to provide a breather arrangement for the internal combustionengine which will be fully outlined below. Further, the radial aperture154 may be found in a radial disc (not shown) attached to the cam shaftassembly 106 in close proximity to the gear 104 so as to be incommunication with the passageway 152 and crank chamber 124.

[0087] As shown, the cam shaft 98 is located normal to the crankshaft80. As can be appreciated by those skilled in the art, generally, intypical small gas engines, the cam shaft and the crankshaft are parallelto one another, not normal as shown according to the present invention.A parallel arrangement leads to a wider engine whereas the normalarrangement according to the present invention leads to a longer enginedesign with the crankshaft axis being substantially parallel to thelongitudinal axis of the tool. A longer unit is particularly desirablefor those hand-held applications such as power trimmers which requirebetter balance for ease of operation. A wider engine may tend to causethe unit to want to rotate in the operator's hands during use.

[0088]FIG. 2 shows that cam shaft 98 sits in bushings 94 and 96 whichrest in respective pockets within the crank chamber 124 in enginehousing 28. The worm-helical or spiral gears 74 and 104 (FIGS. 2 and 3)are preferably designed such that when cam shaft 98 is placed generallynormal to crankshaft 80, the gears 74 and 104 mesh so that therotational relationship between the crankshaft 80 to cam shaft 98 is 2to 1.

[0089] The tappets 112 and the intake valve 52 and the exhaust valve 54cooperate with cam shaft 98 (FIG. 2). Intake valve 52 and exhaust valve54 are positioned within engine housing 28 adjacent to piston 48 andpiston bore 50. The valves 52 and 54 are positioned such that the valveheads are closer to the centerline of the bore 50 as compared to thelower portions of the valves (FIG. 3). Preferably, the valves 52 and 54are set at an angle of approximately between zero and eight degrees froma line parallel with the centerline of the bore. The intake valve seat56 and the exhaust valve seat 58 are placed within engine housing 28 andcooperate with the heads of the respective valves 52 and 54 toalternately create a seal or an opening into the combustion chamber 39with respect to the ports 41 and 45. The valve spring keepers 62 andvalve compression springs 60 are positioned within the valve chamber 156(FIG. 2). Each tappet 112 includes a respective head 158 which is inoperational contact with respective cam lobes 100 and 102. As the camshaft 98 rotates by virtue of drive gear 74, cam lobes 100 and 102properly engage tappets 112 such that valves 52 and 54 move up and downas is commonly understood by those skilled in the art.

[0090] With reference to FIGS. 2, 3 and 4, the crank chamber 124 is incommunication with the valve chamber 156 via access passageway oraperture 160. Additionally, the valve chamber 156 is in communicationwith the piston bore 50 via access passageway or aperture 162. Thepassageways 160 and 162 allow valve chamber 156 and the componentstherein to receive lubricant during operation of the engine 20 insubstantially any attitude. Additionally, during storage, with the aidof divider 116, the extended piston bore 50, and the slots 118, 120 and122, a significant amount of lubricant will not remain or flow into thevalve chamber 156.

[0091] Referring to FIGS. 1, 2 and 3, cylinder head gasket 40 ispositioned between the cylinder head 38 and the engine housing 28 so asto provide a proper seal between the two. Spark plug 114 projects intothe enclosed combustion chamber 39. Spark plug 114 fires in combinationwith the ignition coil and magneto (not shown) to provide the necessarycharge or high voltage signal to ignite the air/fuel mixture in thecombustion chamber 39 when the engine 20 is in operational mode.

[0092]FIGS. 10 and 11 schematically show, at least in part, thecombustion chamber 39 with respect to the intake valve 52, exhaust valve54 and piston bore 50. As shown, the combustion chamber 39 onlypartially extends over the piston bore 50. The orientation of thecombustion chamber 39 and shape of the combustion chamber 39 enhancesswirl in the mixing chamber 39 so as to provide a better air/fuelmixture to enhance ignition of the mixture. Also, the spark plug 114 ispositioned closer to the exhaust valve 54 than it is to the intake valve52. The electrode 164 is properly oriented to provide a firing spark.Placing the spark plug 114 nearer the exhaust valve 54 allows the hotterair/fuel mixture to be burned sooner by the spark ignited flame front.This will reduce the self-ignition tendency of the hotter air/fuelmixture at the exhaust side of the combustion chamber 39. If the sparkplug 114 is positioned closer to the intake valve 52, there is a risk ofhaving two combustions, resulting in a loss of power.

[0093] As shown in FIG. 2, the intake port 41 and the exhaust port 45are located 180 degrees apart from each other. The position of thevalves 52 and 54 is a result of the substantially normal arrangement ofthe cam shaft 98 and crankshaft 80 and allows the ports 41 and 45 to bepositioned on opposite sides of the engine housing 28. This provides anadditional feature of operator safety. For example, when using a powertrimmer, the exhaust port 45 and muffler 44 (FIG. 1) are positionedfarther away from the operator during use. Another advantage of placingthe ports 41 and 45 as far apart as possible is to reduce heat migrationfrom the exhaust port 45 to the intake port 41 which, if did occur,could result in hot restart vapor lock issues, or difficulty incalibrating the air/fuel ratio.

[0094]FIG. 12, with reference to FIGS. 2 and 10 as needed, shows aschematic representation of the path traveled by the air/fuel mixtureand exhaust through the engine 20. The air/fuel mixture enters theintake port 41, travels past the intake valve 52, and into thecombustion chamber 39. The engine 20 combusts the air/fuel mixture inorder to generate power, and the remaining exhaust travels past theexhaust valve 54 and out the exhaust port 45. The arrangement of the camshaft 98 and the crankshaft 80 is also shown to illustrate how such anarrangement contributes to the overall scheme associated with theair/fuel and exhaust paths through the engine 20.

[0095] An important feature of the present invention is that thefour-stroke engine according to the present invention is capable of usein substantially any position. A problem with prior conventionalfour-stroke engines is that if the engine is substantially tilted, thelubricant will run into undesirable locations, such as the carburetor,thereby causing the engine to malfunction or cease working altogether.The four-stroke engine according to the present invention is designed tosolve this problem and other problems typically associated withconventional four-stroke engines.

[0096] The oil or lubricant reservoir 126, the crank chamber 124, thepiston bore 50, and the valve chamber 156 include strategically placedslots, passageways, or apertures so as to enable various workingcomponents within the engine to be lubricated at virtually all timesduring operation. Additionally, in cooperation with the divider 116, thecounterweight 76 has been designed such that only a proper amount oflubricant comes into contact with the counterweight 76. The design ofthe counterweight 76 also allows the counterweight to meter the amountof lubricant that finds its way to the main bearing 70 so as not toflood that part of the crank chamber 124 encapsulating the gears 74 and104. This also will help prevent too much lubricant from entering thevalve chamber 156 through passageway 160 and 162. Moreover, the pistonbore 50 and divider 116 have been designed to ensure that the lubricanthas a place to go regardless of whether the engine is operating or beingstored, so as not to foul the internal components of the engine.

[0097] The piston bore 50, connecting rod 84, the crankshaft assembly82, the cam shaft assembly 106, and the valve chamber 156 and thecomponents therein all require some lubrication. It is a feature of thepresent invention to use a minimal amount of lubricant or oil tolubricate the engine. This is accomplished in a number of ways. First,the highest part that needs lubrication, considering when the engine isin an upright (spark plug up) condition, is the valve chamber 156.Second, the roller bearings 86 and 88 for the connecting rod 84 requireless lubrication versus a solid shaft with aluminum bushings. Third,since the lubricant will follow the path of least resistance, thedivider 116, the counterweight 76 and the various slots, apertures andpassageways previously mentioned help direct the lubricant to particularareas of the engine depending on the attitude of the engine.

[0098] In an upright non-operating position, lubricant or oil is storedwithin the oil or lubricant reservoir 126. In this position and in thisstate, the level of the lubricant is preferably below the bottom slot118 in the divider 116. During operation, the reciprocating movement ofthe piston 48 creates pressure pulses within the internal cavity of theengine 20. The lubricant moves in response to the movement of the piston48. The counterweight 76 agitates the lubricant or oil and blow-by gaswithin the inside cavity of the engine 20. As the piston 48 travels inits downward direction during the intake and power strokes, thelubricant is forced through the main bearing 70 to lubricate thebearings 70 and 68, the worm-helical or spiral gears 74 and 104, thecrankshaft 80, the cam shaft 98 and the bushings 94 and 96 due toincreased pressure in the engine cavity. The action of the cam gear 104will cause some lubricant to enter aperture 160 and migrate to the valvechamber 156. Moreover, any oil found in piston bore 50 could be pushedinto aperture 162 to also lubricate the valve chamber 156. On the upwardstrokes, i.e., the compression and exhaust strokes, the lubricant willbe drawn back over the just mentioned areas to further lubricate thecomponents due to a partial vacuum in the engine cavity. Thereciprocating movement of the piston 48 moves the lubricant back andforth within the internal cavity of the engine 20. The invention doesnot require a control valve to control movement of the lubricant.

[0099] There are at least a couple of aspects to consider whendiscussing lubricating the engine 20. First, there is resistance orenergy lost as the counterweight 76 agitates the lubricant and blow-bygas. Second, it is undesirable to supply too much lubricant to thepiston bore 50 and the valve chamber 156 which, if did occur, couldresult in damage to the engine 20.

[0100] As noted, since the static oil level is preferably below thebottom slot 118 in an upright condition, the counterweight 76 preferablydoes not dip directly into the lubricant, although direct dipping couldbe used. The more direct contact made with the lubrication, the moreenergy that is lost from the engine 20. The least amount of lubricantresistance is desired. As mentioned, the counterweight 76 is designed tothrow the lubricant away from the main bearing 70 and towards the sumpcover 32. The design of the counterweight 76 also limits the amount oflubricant slung into the piston bore 50. In this way, only a limitedamount of oil will find its way to the valve chamber 156. Thecounterweight 76 is designed to reduce the amount of drag that thecounterweight 76 has when it is rotating through and churning up thelubricant. In addition, the counterweight 76 design reduces windagewhich creates a more efficient engine. It should be noted that althoughthe counterweight 76 is shown and described as the device which agitatesthe lubricant and blow-by gas within the internal cavity, a separateagitator may be provided to accomplish the same results. Such anagitator may be a splasher or mixer attached to the rotating crankshaftor connecting rod, or caused to rotate in any number of other ways.

[0101] In an upside down (spark plug down) position such as that shownin FIG. 13, the extended piston bore 50, the divider 116, the slots 118,120 and 122, and the passageways 160 and 162 (FIGS. 2 and 3) ensure thatthe engine will continue to function properly, for at least a limitedamount of time, or be capable of storage in this position withoutfouling the engine. During operation, the changing pressure pulses, theblow-by gas and the agitator 76 will cause the lubricant to be mixed andmoved inside the cavity of the engine 20. Although some oil will beflung into the piston bore 50, not a significant amount will go there.Also, it should be noted that the access passageway 162 is located suchthat the oil ring 166 in the piston 48 does not travel over or past thepassageway 162 as the piston 48 reciprocates within the piston bore 50(FIG.5). Otherwise, it would be possible for lubricant found within thevalve chamber 156 to find its way into the combustion chamber 39,thereby burning off the lubricant and creating excess emissions.

[0102] The crank chamber 124 includes the area or space 136 between theextended piston bore 50 and divider 116 for receiving oil or lubricantwhen the engine is tilted or inverted as representatively shown in FIG.13. During storage, the slots 118, 120 and 122 will allow most of theoil to remain in the oil reservoir 126, and the area 136 between thedivider 116 and the piston bore 50 will hold most of the remaininglubricant. Any oil left in the valve spring chamber 156 during use isthought to be negligible and will not significantly affect the operationof the motor. Importantly, because of the positioning of the slots 120and 122 above the oil in the inverted position, the valve chamber 156will not be able to receive any significant amount of oil.

[0103] To further explain certain features of the present invention, theoil reservoir 126 should be in communication with the crank chamber 124so as to allow for proper lubrication of the engine 20 in substantiallyany operational position. The various described slots, passageways,holes and apertures perform at least two functions. First, if the engine20 is operating in a sideways condition, the slot 120 or 122 in thedivider wall 116 facing down towards the ground allows oil to travelinto the crank chamber 124 with the pressure pulsations in a mannersimilar to when the engine is in an upright state during which lubricantmoves through the bottom slot 118. Second, if for whatever reason, asignificant amount of lubricant finds its way to the crank chamber 124during operation and the engine 20 is turned off and turned upside downor sideways for storage, the side slots 120 and 122 allow oil to migratefrom the crank chamber 124 to the oil reservoir 126 so as to prevent thepiston bore 50 and valve chamber 126 from undesirably receiving asignificant amount of lubricant.

[0104] Another important feature of the present invention is to be ableto vent blow-by gas from the crank chamber 124 by separating the blow-bygas from the lubricant/blow-by gas mixture. As described, the cam shaft98 is provided with a hollow passageway 152 and properly positionedradial passages 154. With reference to FIG. 2, one end of the cam shaftcover 108 includes a nipple 168 which is attached to a flexible hose 170(schematically shown). Although not shown, there may be an oil sealplaced between the cam cover 108 and engine housing 28. As the pressurepulse forces the lubricant/blow-by gas mixture through the main bearing70, the blow-by gas is driven into the radial holes 154 and passageway152 while the oil is prevented from passing through the holes 154 as aresult of the centrifugal action of the operating cam shaft 98. Theblow-by gas travels through the cam cover 108 and nipple 168 affixed tocam cover 108, through the flexible hose 170 and back into the intake ofthe carburetor 42. A check valve may be positioned between the end ofthe cam shaft 98 and the air intake system to maintain the negativepressure created within the engine.

[0105]FIG. 14 shows a cross-sectional view of the four-stroke engineaccording to the present invention with a starter mechanism 172 attachedto the sump cover plate 32 with screws 30. A crankshaft adapter 174 isconnected to crank pin 78. A clutch bearing 176 is press fitted aroundthe crankshaft adapter 174. A starter shaft 178 is positioned around theclutch bearing 176 and is keyed or molded to the starter 180. An oilseal or O-ring 181 is placed around the starter shaft 178 to provide aseal between the starter mechanism 172 and the sump cover 32. A thrustwasher or bearing 182 is placed on each side of the starter 180. Starter180 is preferably a rewind starter having a pull cord 184. Locating thestarter mechanism 172 or the sump cover 32 on the back of the engine 20enables the operator to have easy access to the pull cord. Further,integrally connecting the starter to the piston 48 through connectingrod 84 and the crankshaft 80 through the crank pin 78 reduces the ropepull force needed to start the engine 20. Alternatively, other starterassemblies may be utilized.

[0106]FIGS. 15-18 depict a layout for the dies used to manufacture anengine housing according to the present invention. The engine housing isdesigned to permit two engine housings to be produced using one die tooland one die casting machine. The engine housing is designed to includewalls which allow for the needed draft angles given differentorientations for each engine housing within the die tool. The draftangles enable the engine housing to readily separate from the die. Theengine housing is designed to permit slide tooling access (i.e., thepiston and cam shaft bores) when two engine housings are fabricated fromone tool. In FIGS. 15-18, the dies 188 and 190 are formed so that thecenterlines of the engine cylinder bores (which are parallel todirection C) are parallel to each other. Boxes 194 and 196 represent theedges of the tool. By positioning the dies in this manner, the insertsused to form the dies are inserted only along a few directions, i.e., indirections A, B and C. This die configuration reduces the overall spacerequired to make the engine housings, while still enabling two enginehousings to be made at the same time. The two die halves 188 and 190 areparted along parting line 192. It should be noted that the back wall ofthe engine housing is not shown and is separately formed and thenfastened to the engine housing with bolts or other suitable fasteners.It is, however, possible that the back wall could be formed integralwith the engine housing according to the principles set forth above. Itshould also be noted that the parting line 192 could be moved to anotherlocation. The draft angles of the engine housing outer walls wouldchange accordingly so as to accommodate the new location of the partingline.

[0107]FIGS. 39-40 depict another embodiment of a layout for the die 529used to manufacture an engine housing according to the presentinvention. In this embodiment, it is still possible to permit two enginehousings to be produced using one die tool and one die casting machine.The die 529 is laid out in such a manner that the centerlines of thepiston bores are parallel but in opposite directions. Further, bothcavities are oriented such that the stationary bodies of materialcompose the internal features of the oil reservoir, the barrier wall andthe inner crank chamber. The engine housing is designed to include wallsof which are needed for draft angles parting line jumps, and slideshut-offs for the given orientation within the die layout. By orientingthe die in such a prescribed manner, the inserts for the die pieces areinserted only along a few directions, i.e., in directions D, E, F and G.This embodiment of the die layout also serves to minimize the overallspace necessary to manufacture the two-engine housings out of a singledie.

[0108] With such a die layout, the datum targets or reference featuresfor both cavities are created by the same piece of stationary material.By having these references on the same piece of stationary material,there is less variance to accommodate between the casting in themachining of the finished engine housing. This further translates intoless variance in the finished-machined engine housing even though thecasting is being derived from two separate cavities.

[0109] As shown, this embodiment also integrally creates the flywheelback-plate into the engine housing casting. It is further desirable togate 531 the casting into the deck of the cylinder and route the gatesparallel to directions F and G into the cavities.

[0110] The engine 20 shown in FIG. 1 has been described in such a mannerto identify the various aspects of the present invention. However, thefeatures of the present invention described above may be incorporatedinto other four-stroke internal combustion engine configurations.Moreover, the features identified above may be slightly modified toaccommodate different engine designs. As such, FIGS. 19-40 illustrateanother four-stroke internal combustion engine in which the featurespreviously described may be employed and which incorporates additionalinventive features not yet previously described. It should be noted thatthe features specifically described in relation to FIGS. 19-40 may beincorporated into the engine described in FIGS. 1-18, or other engines.

[0111]FIG. 19 illustrates a four-stroke internal combustion engine 300according to the present invention. The engine 300 is shown as used in apower trimmer but may be used in other devices as described for theengine of FIG. 1.

[0112] Again, before describing in detail the various features of thepresent invention, the components shown in FIGS. 21 and 22 areidentified for the sake of clarity. Many of the components are assembledin the same or similar manner as described in reference to FIG. 1 or asgenerally understood by those skilled in the art. Accordingly, themanner of assembly is not described in great detail below except if themanner of assembly pertains to specific features of the presentinvention. Greater detail of such features will be provided in referenceto the drawings to follow when needed. Shown in FIG. 21 are spark plug302; cylinder head screws 304; cylinder 306; cylinder head gasket 308;compression rings 310 and 312 and oil ring 313 which are appropriatelypositioned in annular slots located in piston 314; connecting rod 316and connecting rod bearings, preferably needle roller bearings, 318 and320; exhaust valve 322, intake valve 324, valve springs 326 and valvespring keepers 328; engine housing 330; valve cover 332 and associatedscrews 334; flywheel 336, crankshaft adapter 338, ignition coil 340,wiring assemblies 342 and 346, and screws 344 all of which are part of astarter assembly; muffler mounting bolts 350; muffler 352; and blowerhousing 348 which is part of an overall shroud further described below.

[0113] Shown in FIG. 22 are sealing O-ring 366 and oil gauge 367; intakegasket 368, intake isolator 369 and screws 370; carburetor gasket 372,carburetor 374 and O-ring 376; air filter assembly 378, screws 380 andair filter cover 382; wrist pin 384 and star washer wrist pin retainer386; oil sealing ring 388, roller bearing 390, crankshaft 392 andcounterweight 393; sump cover 394 and screws 396; muffler housing 398which is part of an overall shroud further described below and mountingscrews 400; tappets 402, cam shaft 404, cam shaft cover 406; screws 408and breather tube 410; check valve 411; fuel tank 412 having fuel line414, opposing shoulders 416; and filter material 418 which is placedaround shoulders 416 as further described below.

[0114] Other components and features not clearly shown in FIGS. 21 and22 will be described below. Moreover, the significance of any of thecomponents shown in FIGS. 21 and 22 or their interaction, will bedescribed below in conjunction with the principles of the presentinvention.

[0115]FIG. 23 more clearly shows the engine housing 330 with the muffler352 attached thereto by mounting bolts 350. The engine housing 330includes a crankcase 420 and a cylinder 422. The cylinder head 306 (FIG.21), which at least partially defines a combustion chamber, is disposedadjacent to the cylinder 422. A crank chamber 426 is disposed within thecrankcase 420. An oil reservoir 428 is also disposed within thecrankcase 420 and is in fluid flow communication with the crank chamber426, preferably, through slot 430 and opposing holes 432 (only one beingshown) disposed in a divider 433. The divider 433 is disposed within thecrankcase 420 and at least partially divides the crank chamber 426 andthe oil reservoir 428. A plurality of holes 434 are provided in theengine housing 330 so that the sump cover 394 and sump cover gasket canbe attached thereto. The engine housing 330 also includes an oversizedwrist pin boss 436. The wrist pin boss 436 may be integrally formed withthe divider 433. The function of the wrist pin boss 436 will be furtherdescribed below. The engine housing 330 also includes a flywheel backplate 438 with at least one mounting boss 440, the function of whichwill be described below.

[0116]FIG. 24 is an exploded perspective view of FIG. 23 showing how themuffler 352 is connected to the engine housing 330. The cylinder 422includes an exhaust port 442 and an intake port 444 (FIG. 25).Preferably, the intake port 444 and exhaust port 442 are elliptical inshape thereby enabling the overall height of the engine housing 330 tobe reduced. This will naturally reduce the overall weight of the enginehousing, which is an especially important factor for hand-held powertools. The walls of the ports 442 and 444 are provided with sufficientmaterial so as to be able to support the weight of the engine housing330 and cylinder head 306 disposed thereabove.

[0117] The muffler 352 includes a boss 446 which is preferablyelliptical. The boss 446 extends into the exhaust port 442. Mountingbolts 350 extend through holes 448 in the muffler 352 and into holes 450formed in the cylinder 422. Preferably, the holes 448 are spaced apartand positioned on opposite sides of the exhaust port 442 to maximize thestability of the muffler 352 with respect to its connection to thecylinder 422.

[0118]FIGS. 26 and 27 are enlarged partial cross-sectional views takenalong line 26-26 of FIG. 23 showing preferred alternative mountingconnections between the muffler 352 and cylinder 422. FIG. 26 shows theengine housing 330 having an angled, step sealing surface 452 located inthe exhaust port 442 of cylinder 422. The end 454 of boss 446 can mateagainst the exhaust port sealing surface 452 to substantially preventexhaust from undesirably escaping into the environment. Preferably, asealing gasket 456 is positioned between the end 454 of the boss 446 andthe sealing surface 452 to even better prevent the exhaust fromescaping.

[0119]FIG. 27 shows the outside liner of the boss 446 of the muffler 352surrounded by the surface 458 of the exhaust port 442, thereby defininga clearance space 460 therebetween. Although surface 458 is shown as anangled surface, it may take on other configurations so long as clearancespace is provided between the muffler 352 and the exhaust port 442. Agasket 462 is positioned between the muffler 352 and cylinder 422 orengine housing 330 to seal the clearance space 460, thereby preventingexhaust from escaping into the atmosphere. Preferably, the gasket 462 isan enlarged gasket which also serves as a heat shield between the enginehousing 330 and the muffler 352.

[0120] The muffler 352 (FIG. 24) preferably includes a pair of outershells 464 and 466 having respective mounting bolt holes 448 for themounting bolts 350. An inner shell or baffle plate (not shown) ispreferably located between the outer shells 464 and 466. The inner shellalso is adapted to allow the mounting bolts 350 to pass therethrough.The baffle plate is designed to reduce noise. Outer shell 464 includes ashoulder 470 which extends around an edge of the outer shell 464. Outershell 466 includes a flange (not shown) which extends around an edge ofthe outer shell 466. Upon assembly, the shoulder 470 receives the flangesuch that if exhaust does leak out of muffler 352, the exhaust will leakaway from the engine. Although not shown, a deflector may be placed overthe exhaust holes 372 (FIG. 23) of the muffler 352 to protect theoperator from receiving a direct blast of exhaust.

[0121] Given the nature of the four-stroke engine according to theprinciples of the present invention, it is desirable to provide aneconomical engine with features which allow the engine to be easilyassembled. One feature is to use the same engine housing 330 for engineshaving different horsepower ratings, simply by changing the connectingrod 316 (FIG. 21) and thus, the length of the piston throw. Toaccomplish this feature, the oversized wrist pin boss 436 (FIG. 23) isprovided. The wrist pin boss 436 can be machined at its upper end 474 toprovide an access hole (not shown) in the crankcase 420 for a firstpiston throw, and the wrist pin boss 436 can be machined at its lowerend 476 to provide an access hole (not shown) in the crankcase 420 for asecond piston throw. After the wrist pin boss 436 is properly machined,the wrist pin 384 (FIG. 22) is inserted through the crankcase accesshole and into the piston access hole to connect the piston 314 (FIG. 21)to the connecting rod 316 (FIG. 21). Accordingly, the same enginehousing 330 can be used for different sized engines. FIG. 31 shows acompleted assembly on such engine. FIG. 32 shows the piston 314 in itsbottom most dead center position so that the wrist pin 384 can beappropriately positioned within the engine.

[0122]FIG. 28 is an enlarged view of the engine housing 330 of FIG. 24without the muffler 352. As shown, the divider 433 defines a path 478which extends substantially about the divider 433 and over the wrist pinboss 436. The path 478 allows lubricant found in the oil reservoir 428to flow around a substantial portion of the divider 433 to furtherenhance the lubricating and storage features according to the principlesof the present invention. The path 478 allows the amount of lubricantfound on both sides of the divider 433 to equalize when the engine 300is turned upside down. This further inhibits a substantial amount of thelubricant from migrating into the crank chamber 426.

[0123] Another feature which reduces assembly costs of the enginethereby reducing the overall cost of the engine relates to the manner ofassembling a shroud to the engine housing. As noted with reference toFIG. 23, the flywheel back plate 438 is provided with at least onemounting boss 440. FIG. 25 is a perspective view of the engine housing330 of FIG. 23 only from a different perspective. As shown, the oppositeside of the flywheel back plate 438 also includes at least one mountingboss 480. Upon assembling the engine 300, an assembly fixture (notshown) is adapted to hold the engine 300. Each mounting boss 440 and 480receives a separate pin (not shown) of the assembly fixture to securethe engine housing 330 to the assembly fixture. A shroud 482 (FIG. 20)is provided to at least partially surround the engine housing 330.Preferably, the shroud comprises the blower housing 348 (see also FIG.21) and muffler housing 398 (see also FIG. 22). Shroud 482 includes atleast one slot 484. Each slot 484 is designed to surround a respectivepin of the assembly fixture extending out of the mounting bosses 440 and480 when the shroud 482 is positioned around the engine housing 330. Theshroud 482 can be attached to the engine housing 330 by threading screws486 (FIG. 20) into respective holes such as hole 488 (FIG. 25) of theengine housing 330. Thus, the entire engine 300 can be substantiallyassembled while remaining attached to a single assembly fixture.

[0124] Another feature of the shroud 482 is that the muffler housing 398preferably includes a plurality of raised portions 490 (FIG. 31). Thus,if desired, the engine 300 may be placed on the ground to rest on theraised portions 490. It should be noted that the blower housing 492′ ofFIG. 31 is slightly different from the blower housing shown in FIG. 20.The purpose of this is to show that various suitable configurations ofthe shroud 482 are possible without affecting the scope of the presentinvention.

[0125] As shown in FIG. 20, the shroud 482 is provided with an opening494 which surrounds the intake port 444 (FIG. 25). An intake isolator369 (FIG. 22) having an air/fuel passageway 496 (FIGS. 29 and 30)extending therethrough is provided. The intake isolator 369 is mountedto the engine housing 330 so that the air/fuel passageway 496 is alignedwith the intake port 444. The intake isolator 496 is positioned withinthe opening 494 of the shroud 482 to substantially ensure that coolingair passing between the engine housing 330 and the shroud 482 cannotescape through the opening 494 in the shroud 482. Preferably, the intakeisolator 369 includes an integrally formed back wall 498 and a side wall500 (FIG. 22) to accomplish this feature.

[0126] To further reduce manufacturing costs, the crankcase 420, thecylinder 422 and the back plate 438 are cast as a single component. In apreferred embodiment, the engine housing 330 further includes at leastone fin 502 integrally formed thereto (FIG. 28). The fin 502 extendsfrom the back plate 438 and beneath the crankcase 420 for stability andcooling purposes.

[0127] Although the shroud 482 may be of many different designsconsistent with the principles of the present invention, the shroud 482is designed to hold the fuel tank 412. As best shown in FIG. 31, theshroud 482 is provided with a pair of opposed channels 504 (only one isshown). The outwardly extending shoulders 416 (see also FIG. 22) arereceived by the respective channels 504 so that the fuel tank 412 isheld by the shroud 482. The filler material 418 (see also FIG. 22),preferably a polyethylene, high-density, closed cell, high-temperatureand gasoline-resistant foam material, is positioned between each channel504 and the respective shoulder 416 to provide a tight fit between theshroud 482 and the fuel tank 412. The fuel line 414 (FIG. 22) includes afuel filter 506 attached to the end of the fuel line 414 disposed withinthe fuel tank 412. It should be noted that the extra line shown in FIG.22 is a purge line. The fuel filter 506 acts as a weight such thatduring operation of the engine, if the engine is tipped, the weightedfuel line 414 swings to the bottom of the fuel tank 412 to ensure thatfuel is picked up by the fuel line 414.

[0128] Another aspect of the present invention concerns the starterassembly 507 shown in FIG. 33. The blower housing 348 is provided with ahub 508 having an inwardly facing extension 510. The hub 508 is adaptedto fit over the crankshaft 392 (FIG. 22) or crankshaft adapter 338 (FIG.21). The starter assembly 507 which includes the pulley 516, rope 518and spring 520 is positioned onto the hub 508. A star washer 514 isplaced over the hub extension 510 so as to dig into the extensionmaterial. The star washer 514 holds the starter assembly 507 in placewith respect to the blower housing 348. This arrangement eliminates theneed for separate mounting bosses and fasteners typically needed to holdthe starter assembly in place. Such mounting bosses and fastenersgenerally block the cooling air flow by a fan.

[0129]FIGS. 34-38 show various views of the pulley 516. The spring 520(FIG. 33) is positioned on one side 522 of the pulley 516 having anappropriately shaped annular recess 524. The opposite side 526 of thepulley 516 includes a plurality of spokes 528 for engagement with aflywheel such as flywheel 336 shown in FIG. 21. The rope 518 includes aknot 530 on one end thereof which is held in a chamber 532 formed in ahub 534 of the pulley 516 beneath the pulley rope portion 536. The rope518 extends through a hole 538 in the pulley rope portion 536 and iswrapped around the pulley 516. The other end of the rope 518 is attachedto a starter handle 540 (FIG. 20).

[0130] The foregoing description of the present invention has beenpresented for purposes of illustration and description. Furthermore, thedescription is not intended to limit the invention in the form disclosedherein. Consequently, variations and modifications commensurate with theabove teachings in skill or knowledge of the relevant art, are withinthe scope of the present invention. The embodiments described herein arefurther intended to explain the best modes known for practicing theinvention and to enable others skilled in the art to utilize theinvention as such, or other embodiments and with various modificationsrequired by the particular applications or uses of the presentinvention. It is intended that the appended claims are to be construedto include alternative embodiments to the extent permitted by the priorart.

[0131] Various features of the invention are set forth in the followingclaims.

What is claimed is:
 1. A four-stroke internal combustion engine,comprising: an engine housing including a crankcase and a cylinder; acrank chamber disposed within said crankcase; a crankshaft supported forrotation within said crank chamber; a piston operably interconnectedwith said crankshaft for reciprocation within said cylinder in responseto rotation of said crankshaft; an oil reservoir disposed within saidcrankcase, and in fluid flow communication with said crank chamber; anarcuate divider at least partially separating said crank chamber fromsaid oil reservoir; and a depending wall extending at least partiallyinto said crank chamber to define a lubricant receiving space betweensaid divider and said depending wall.
 2. An engine as set forth in claim1, wherein said divider includes an opening, such that said crankchamber and said oil reservoir are in fluid flow communication throughsaid opening.
 3. An engine as set forth in claim 2, wherein said dividerfurther includes a second opening and a third opening, said secondopening positioned substantially across from said third opening, saidcrank chamber and said oil reservoir being in fluid flow communicationthrough said second and third openings.
 4. An engine as set forth inclaim 1, wherein said depending wall is a cylinder side wall.
 5. Anengine as set forth in claim 1, further comprising an intake valve andan exhaust valve disposed within the engine housing to the side of thecylinder, wherein said engine housing further includes a valve chamberin which said intake valve and said exhaust valve are disposed, saidvalve chamber being in fluid flow communication with said crank chamber.6. An engine according to claim 1, further comprising: a cam shaftrotatably driven by said crankshaft and oriented substantially normalwith respect to said crankshaft.
 7. An engine according to claim 6,further comprising first and second valve tappets associated with arespective valve and operatively engaging said cam shaft, wherein saidvalves are disposed substantially normal to said crankshaft.
 8. Anengine according to claim 6, wherein said cam shaft has an axialpassageway and a radial aperture communicating between said crankchamber and said passageway, said engine further comprising a breathertube having one end communicating with said passageway of said cam shaftand another end communicating with an air intake system of said engine.9. An engine according to claim 1, wherein said crankshaft iscantilevered, said crankcase includes an access hole, said pistonincludes an aperture, said access hole and aperture being alignableduring assembly of said engine; and wherein said engine furthercomprises: a connecting rod having one end pivotally attached to saidcrankshaft and the other end pivotally connected to said piston; and awrist pin insertable through said access hole and into said aperture insaid piston to pivotally connect said connecting rod to said piston. 10.An engine according to claim 1, wherein said crank chamber includes atleast two bearing pockets, one pocket having a larger diameter than theother and both pockets being disposed on the same side of said dependingwall.
 11. An engine according to claim 1, further comprising a shroud atleast partially surrounding said engine housing and including a pair ofopposed channels, and a fuel tank having opposed outwardly-extendingshoulders, such that said shoulders of said fuel tank are received bysaid respective channels of said shroud.
 12. An engine according toclaim 1, wherein said engine housing further includes a back plate whichis adjacent to a flywheel, and wherein said crankcase, cylinder, andback plate are cast as a single component.
 13. An engine according toclaim 1, wherein said cylinder includes elliptical intake and exhaustports on opposite sides of said engine housing, and intake and exhaustvalves in communication with said intake and exhaust ports,respectively.
 14. An engine as set forth in claim 1, wherein the divideris substantially U-shaped.
 15. An engine as set forth in claim 14,wherein one side of the divider is exposed to the oil reservoir and anopposite side of the divider is exposed to the crank chamber.
 16. Theengine of claim 1, wherein said cylinder defines a bore having a boreaxis, and wherein said depending wall extends into said crank chambergenerally parallel to said bore axis.
 17. The engine of claim 1, whereinsaid cylinder defines a bore, and wherein said depending wall defines anextension of said cylinder bore into said crank chamber.
 18. The engineof claim 17, wherein said bore extension and said cylinder bore havesubstantially the same diameter.
 19. The engine of claim 18, whereinsaid bore extension and said cylinder bore are substantially coaxialwith each other.
 20. The engine of claim 1, further comprising acylinder head mounted to said engine housing over said cylinder to atleast partially define a combustion chamber in said cylinder, and intakeand exhaust valves disposed within said engine housing.